LOL, yeas, lots of marshmellows.
As for the structure, I can really jump on the thing, no problem at all. With the sod on top it will weight some, but also distribute the weight that definately gets added by ...kids.
And the water normally does not penetrate 3 layers of turf. If it does, the top and sides are covered with tar paper and the sides as well. The roof has a flap extending into the top turf, practically to the side of it. The idea is that IF water gets through, it must also be able to exit. I have used the trick before and it workd, but that roof is steeper.
More pics upcoming soon.